Circuit for audions



April 13 1926.

J. F. FARRINGTON CIRCUIT FOR AUDIONS 'Fil-ed oct. 25 1920 Patented Aar.13, 1926.

UNITED STATES 1,580,427 PATENT OFFICE.

JOHN F. FARRINGTON, OI NEW YORK, N. Y., ABSIGNOR T WESTERN ELECTRIC COM-IPANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION 0F NEW YORK.

CIRCUIT FOR AUDIONS.

Application filed October 25, 1920. Serial No. 419,518.

To all whom it may concern:

Beit known that I, JOHN F. FARnnyG'roN, a citizen of the United States,residing at New York, in the county of the Bronx,

State of New York, have invented certain new and useful Improvements inCircuits for Audions, of which the following is a full, clear, concise,and exact descriptlon.

The invention relates to circuits for elec- '10 tric space dischargedevices and especially to improvements in that part of the circuit shownin White Patent No. 1,195,632, which relates to heating the filamentarycathode of electron discharge devices.

According to the disclosure in that patent, the source of alternating.current for heat-.- ing the filament is connected to the cathodesthrough a transformer. The grid and anode electrodes are connected tothe midpoint of the secondary winding of this transformer in order thatthere ma be introduced into the circuit no fluctuations of a frequenccorresponding to an audible frequency suc i as 60. cycles which isemployed for heating i the filaments. By this arrangement 'the averagedifference of potential at any instant between the three electrodes isindependent of the potential applied to the cathode for heatingpurposes. According to the disclosure in the patent, in case the natureof the circuit is such as to require a plurality of electron dischardev1ces, a separate transformer winding aving a midpoint connection isprovided for the cathode of each vacuum tube. Y

According to the present invention, only a single transformer need beemployed in the filament 'lighting circuit, even though filaments of aplurahty of-vacuum tubes are 40 required to be heated. Thisis'accomplished A by providing a compensating circuit which is common toall of the vacuumv tubes. Specifically this arrangement comprises animpedance connected 1n shunt to the secondary winding-of thetransformer, the grid and anode electrodes of all the vacuum: tubescompletin their circuits through the midpoint of t ls impedance.

A further object of the invention is to employ a pluralit of electrondischarge devices having di erent filam'ent resistances in connectionwith a source of alternating current for heating the filaments and insuch a manner that the current fiowing to the tube 55. or tubes of lowfilament resistance may be reduced without unbalancing the averageldifference 1n potential between the cathode and its associated grid andanode. This is l accomplished by connecting the filaments in parallel tothe terminals of the transformer secondary, which is com nsated as abovedescribed, and by dividing the resistance which is to reduce thefilament current flowing to one or more tubes into two equal parts, eachof which is placed in one of the filament leads. The center of thisfilament then has-an average zero potential as in the other cases. i

A further object of facilitate maintenance of a proper value of voltagebetween the anode and cathode vof an electric space discharge device.This is accomplished by a suitable arrangement of impedances in thecircuit ofthe space current source.

The invention will be described in further the invention is yto I detailin connection with the drawings, in

which the figure'illustrates diagrammatically a radio transmittingcircuit embodying the invention.

Referring in detail to the drawings, the circuit chosen toillustrate theinventiomis a radio transmitting circuit, although the schemeof lightingthe filaments may be applied to any type of circuit.

In the figure the vacuum tube 1 is a speech current amplifier formodulating by means of the tube 2 the .high frequency currents which aregenerated by the tube 3 and amplified bythe tube 4. The modulatedcurrent is supplied to the radiating system 5. The modulating tone maybe derived from the transmitter 6 in circuit with the battery 7 and theprimary winding of transformer 8. The secondary winding of thistransformer is shunted by a high resistance 9 of the order of 100,000ohms. One end of resistance 9 is4 connected to the id of vacuum tube 1,the other end belng connected through the battery 10 to ground. The bat-100 tery 10 serves to make' the grid normally either negative orpositive' a desired amount with respect to the cathode. The grid circuitis completed from ground through the midpoint 11 of resistance 12connected in 105 shunt to the transformer 13 in'circut with the A. G.generator 14, which supplies heating current for the filaments. Theresistance 12 should be of a value comparable with Vthe filamentresistance of one of the 110 tubes in order to lnot waste the anodecircuit energy. The current flowing to the filaments may be regulated bythe resistance 15. By grounding the cathode, the capacity to ground ofthe connecting wires is reduced thereby preventing singing of therepeater. Furthermore, since the path to ground is symmetrical, nounbalance can occur due to the use of alternating currentfor heating thefilaments.

Connected to the secondary of the transformer 13 are the leads or busbars 16 and 17, across which are connected the filaments of the varioustubes. In case the filament of the low power tube 1 has a lowerresistance than the filaments of the other circuits, the current to thisfilament may be reduced without introducing any unbalance by employingequal resistances 18 and 19 in the leads of this filament. If thefilaments of the tubes 2, 3 and 4 all have the same resistance, they maybe connected directly across the leads 16 and 17 without the use of theresistances such as 18 .and 19.

The anode circuits of the tubes may be supplied with direct current fromthe generator 20 having the filter 21 in circuit therewith to reduce theeffect of commutator ri ples. One lead from generator 20 is ta en to themidpoint 11, the other lead is taken (a) through high resistance 22 tothe anode of vacuum tube 1, (b) through choke coil 23 to inductance 24and the anode of vacuum tube 2 on one hand and through inductance 25 tothe anode of vacuum tube 4 on the other hand, and (c) through resistance26 and inductance 27 to the anode of vacuum tube 3. Inductance 24 is ahigh frequency choke coil to prevent undesired oscillation of thecircuit.

The high resistance path 28 to ground may be employed to prevent thefull potential of generator 20 from being applied between the cathodeand anode of tube 1 in the event that .(1) the impedance of tube l isaccidentally made infinite due to not closing the filament circuitbefore closing the anode circuit, or (2) the impedance becomes too high(with reference to resistance 22) due to too high a negative potentialon the grid from battery 10. lf'generator 20 supplies 1500- volts, andif tube 1 is built to stand only 500 volts, then resistance 28 should beone-half the value of 22 and both of. them large as compared to thenormal operating impedance of the tube. In one case a tube has beenemployed corresponding totube l and having a cathode-anode impedance ofabout 5000 ohms, resistance 22 being 30,000 ohms, and resistance 28,15,000 ohms. Tubes 1 and 2 are separated for direct current by theblocking condenser 29. The grid circuit for tube 2 may include a chokecoil 30 connected through battery 31 to ground. Between the grid andanode .quency and offer high impe of oscillator 3 may be connectedcondensers 32 to 29 inc., and the midpoint of condensers 33 and 34 isconnected to the cathode of tube 3. The condensers 37, 38 and 39 may beput in or out of circuit by the switch 40. The grid-anode circuit ofoscillator 3 also includes an inductance 41, which may be put in or outof circuit by a switch 42, resistance 43 and inductance 44. The gridcircuit O tube 3 may be completed through inductance 45 and highresistance 46 to ground. The path to ground including condenser 50 hasbeen found to prevent objectionable singing of the circuits.

The amplified modulated high frequency current appearing in the outputcircuit of tube 4 is supplied through the condensers 47 and 48 to thecoil 49, which may be variably connected in the antenna circuit.Condensers 47 and 48 byass high frerequency current.

It will be apparent that the application of the features of theinvention is not limited to the arrangement of discharge devicesspecifically shown in the drawing, and that the vvacuum tubes may beconnected in tandem or in multiple, and these tubes may be employed inany well-known manner as detectors, power limiters or the like withoutbeing restricted to the particular use herein described.

iVhat is claimed is:

1. The combination of a circuit comprising a plurality of electrondischarge devices each having a cathode and an anode, a source ofalternatin current for heating said cath odes, a trans ormer having aprimary winding and a secondary winding for connecting said source tosaid cathodes, and a compensating circuit common to said cathodes forsuppressing the difference in potential between the cathodes and anodesdue to the use of alternating current for lighting said cathodes.

2. A circuit comprising a plurality of electron discharge devicesdelivering electromotive force, each device having a .cathodeadapted tobe connected to a source of alternating current, and a compensatingcircuit common to said cathodes, for preventing the alternations of saidcurrent in said cathodes from causing variations in the electromotiveforce output of said devices.

3. The combination of a plurality of electron discharge devicesconnected in tandem each having a cathode, an anode and a controlelectrode, a source of alternating current for heating said cathodes, atransformer for connecting said source to said cathodes,

an impedance' in shunt to the secondary.

winding of said transformer', and connections rom an intermediate pomtof said impedance to the control electrodes-and anodes of said tubes.

ance for audio Y tubes having a resistance lower than the cathoderesistance of another of said tubes, and means for heating said cathodeswith alternating current while maintaining substantially a zero averagedifference of potential between the cathodes and their respectiveanodes.

6. The combination of a circuit comprising a plurality of electrondischarge devices each havin a cathode and an anode, asource ofalternating current for heating said cathodes, a compensating circuitcommon to said cathodes for suppressing the diference in potentialbetween the cathodes and anodes due to the use of said alternatingcurrent'l for heating said cathodes while permitting said alternatingheating current to heat said cathodes, and means associated with one ofsaid cathodes for reducing the current ow thereto while maintainingsubstantially a zero average diierence `of potential between saidlast-mentioned cathode and its associated anode.

7. A circuit comprising charge device having a anode, a source ofcurrent for heating said cathode, and equal impedances to said current,connecting the terminals of said source to the terminals of saidcathode, respectively.

8. A circuit comprising an electron dis charge device having afilamentary electrode and an anode, means for heating said filamentaryelectrode with alternating current, andequal impedances to said currentin each of the leads of the ilamentary electrode.

9. The combination of a plurality of electron discharge devicesconnected in tandem each having a cathode, an anode and a controlelectrode, a source of alternating current for heating said cathodes, atransformer for connecting said source to said cathodes, an impedance inshunt to the secondary winding of said transformer, connections anelectron discathode and an from an intermediate point of said impedanceto said control electrode and anode, and equal impedances in the leadsof one of said eathodes.

l0. An electron discharge device having an electrode, means -including asource of alternating current and a transformer connecting said sourceand said electrode for heating said electrode by alternating current,and a path to ground for said electrode, said ath comprising aresistance in shunt to said electrode, and a connection from theelectrical midpoint of said resistance to ground.

11. A vacuum tube circuit comprising an electron discharge device havinga cathode, anode and grid electrodes, and means for heating saidcathode, said means including a source of alternating current and atransformer connecting said source and said cathode, and said circuitcomprising also an impedance in shunt to said cathode, a connection froman intermediate point of said impedance to one of said electrodes, and aconnection from an intermediate point of said impedance to ground.

12. A system comprising an electric discharge device having an anode anda cathode, a resistance, a source of electroniotive force for supplyingvolta-ge across said anode and cathode through said resistance, .a loadcircuit for said device,said load circuit` being connected across saidresistance, and means for protecting said device against excessivevoltage from said source, said means comprising a resistance shuntedacross said anode and cathode.

13. A relay system comprising an electron i tube having an anode and acathode, and means for controlling current iow` between said anode andcathode, a resistance having a value high relative to the anode-cathoderesistance of said tube, a source of electromotive force for supplyingvoltage across said anode and cathode through said resistanceta loadcircuit for said tube, said load circuit being connected across saidresist ance, and means for protecting said tube against excessivevoltage from said source, said means comprising a resistance shuntedacross said anode and cathode.

In witness whereof, I hereunto subscribe my name this 23rd day ofOctober, A. D.,

JOHN F. FARRINGTON.

